Fluxgate sensor and electronic compass making use thereof

ABSTRACT

Provided is a flux gate sensor comprising the following: a magnetic core having a first wiring layer formed on a board, a first insulating layer formed in such a way as to cover the aforementioned first wiring layer, and a magnetic core which is formed on the aforementioned first insulating layer and which has a central portion and an end portion that continues to the aforementioned central portion, that has a width larger than the width of the aforementioned central portion, and that is located on either side of the aforementioned central portion; a second insulating layer which covers the aforementioned magnetic core and which is formed on the aforementioned first insulating layer; and a second wiring layer formed on the aforementioned second insulating layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application based on a PCT PatentApplication No. PCT/JP2010/003428, filed May 21, 2010, whose priority isclaimed on Japanese Patent Application No. 2009-123110, filed May 21,2009, the entire content of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a miniature fluxgate sensor that ismanufactured via a thin-film process, and to an electronic compass inwhich this fluxgate sensor is used. In particular, the present inventionrelates to a fluxgate sensor that not only is small in size and ishighly sensitive, but also has a high level of excitation efficiency anda high degree of design freedom, and to an electronic compass in whichthis fluxgate sensor is used.

2. Description of the Related Art

Conventional magnetic sensors include those that utilize the Halleffect, those that utilize a magnetoresistive (MR) effect, and thosethat utilize a giant magnetoresistive (GMR) effect. Because these aremanufactured via a thin-film process, they can be miniaturized andintegrated, and are therefore widely used in portable devices and thelike.

However, the sensitivity of these sensors is lowered when they areminiaturized, and it becomes difficult for geomagnetic levels ofapproximately 0.3 Oe, such as are detected by an electronic compass, tobe detected accurately, and the azimuth accuracy in electronic compassesthat use these sensors is limited to approximately 10 degrees.

Moreover, in recent years, electronic compasses that are based onmagneto-impedance sensors (referred to below as MI sensors) that useamorphous wire, and orthogonal fluxgate sensors have been proposed, andhighly accurate compasses that provide an azimuth accuracy ofapproximately 2.5 degrees have been achieved. In addition, electroniccompasses that use miniature fluxgate sensors that are manufactured viaa thin-film process have also been proposed (see, for example, JapaneseUnexamined Patent Applications, First Publications Nos. 2007-279029,2006-234615 and 2004-184098, and PCT International Publication No. WO2007-126164 Pamphlet).

In order to increase azimuth accuracy, in particular, the detectionresolution and linearity errors that are determined by the sensorsensitivity are important elements. In MI sensors, orthogonal fluxgatesensors, and fluxgate sensors, the resolution is regarded as beingapproximately the same. Moreover, a large number of components such asspeakers, vibration motors, and magnets and the like that serve asmagnetic field generation sources are mounted inside the devices, andthe sensors are affected by the magnetic fields generated from thesecomponents. In order for a sensor to operate correctly in the presenceof a magnetic field generated from a peripherally placed component, itis desirable for the measurement magnetic field range to be sufficientlybroad.

If linearity errors are considered, then in the case of MI sensors andorthogonal fluxgate sensors, hysteresis is also output in the outputvoltage due to hysteresis in the magnetic core. Because of this,linearity errors are made worse. In order to improve linearity, a methodthat utilizes a negative feedback circuit may be used, however, thiscauses power consumption to increase and also makes the circuit morecomplex.

In contrast, in the case of a fluxgate sensor, by using the phase-delaymethod described in Pavel Ripka, “Magnetic Sensors and Magnetometers”,p. 94, ARTECH HOUSE, INC (2001), a magnetic sensor that is not affectedby magnetic core hysteresis and has superior linearity can be achieved.If this method is used, the sensor output is made based on a timedomain, and not only is it possible to remove the effects of hysteresiswhich is caused by the coercive force of the magnetic core that makes upthe sensor, but it is also possible for digital detection using acounter to be made. As a consequence, it is possible to remove theeffects of errors which occur during A/D conversion, and it is possibleto construct a sensor having superior linearity.

According to IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL.42, NO. 2, p. 635, APRIL 1993, by using the aforementioned method, alinearity of 0.06% FS can be achieved. In an MI sensor that usesamorphous wire, linearity errors are 1-2%. Consequently, by using afluxgate sensor having superior linearity in this way, it is possible toachieve an electronic compass having greater azimuth accuracy.

As is described above, by using a fluxgate sensor that employs aphase-delay method which has a high resolution and superior linearity,it is possible to construct an electronic compass having excellentazimuth accuracy. However, it is necessary in a fluxgate sensor for anexcitation coil and detection coil to be wound around the periphery ofthe magnetic core. Accordingly, compared with an MI sensor or anorthogonal fluxgate sensor that are constructed with only a bias coil ora pickup coil being wound around the core, it is difficult to achieve aminiaturization of the size of a fluxgate sensor.

In order to achieve further miniaturization and integration, attemptsare being made to manufacture a fluxgate sensor using a thin-filmprocess. However, the diamagnetic field effect is increased by theminiaturization so that there is a decrease in sensitivity. Inparticular, if this type of sensor is used to try and make an electroniccompass which has sensitivity in three axial directions, then it isnecessary to set a magnetic sensitivity direction in a perpendiculardirection relative to the substrate forming part of the electroniccompass, so that, as a result, it is necessary to package the sensors ina vertically upright state on the substrate used to form the electroniccompass.

As a consequence, when the aim is to make a thinner electronic compass,then it is necessary for the length of the sensor which extendsvertically upright from the substrate to be shortened in the directionof the magnetic sensitivity thereof. For example, if the thickness ofthe electronic compass needs to be kept to 1 mm or less, thenconsidering the thickness of the substrate and the molding resin, it isnecessary to keep the length of the sensor in the direction of magneticsensitivity to approximately 0.5 to 0.7 mm. However, if the length ofthe magnetic core is no more than 1 mm, the effect of the diamagneticfield is increased and there is a marked decrease in sensitivity.

In order to solve the above described problems, Japanese UnexaminedPatent Application, First Publication No. 2007-279029 and PCTInternational Publication No. WO 2007-126164 Pamphlet disclose an H-typeof magnetic core in which the width of the end portions of the magneticcore has been widened. In this structure, the excitation coil and thedetection coil are only wound around the narrow portion of the magneticcore center portion. Accordingly, if the size of the sensor is reduced,the number of coils that can be wound around the excitation coil andmagnetic coil is restricted, and it becomes difficult to secure asufficient number of coils. Because the structure is one in which theexcitation coil and the magnetic coil are wound alternatingly, thenumber of coils ends up being determined by the sensor size and the coilpitch. Accordingly, it becomes difficult to set the number of coils ofboth the detection coil and the pickup coil independently of each other,so that the degree of design freedom is constricted.

FIG. 15 is a schematic view showing the shape of a magnetic core of aconventional fluxgate sensor. The magnetic core has end portions 1 and acenter portion 2. In Japanese Unexamined Patent Application, FirstPublication No. 2007-279029, it is disclosed that a ratio B/A of thewidth B of the end portions 1 shown in FIG. 15 relative to the length Aof the magnetic core in the longitudinal direction is preferably 0.8 to1.2. It is also disclosed that a ratio C/B of the width C of the centerportion 2 shown in FIG. 15 relative to the width B of the end portions 1is preferably 0.033 to 0.2. When the value of the ratio B/D of the widthB of the end portions 1 shown in FIG. 15 relative to the length D of theend portions 1 in the longitudinal direction exceeds 1, then the lengthof the magnetic core in an orthogonal direction relative to the magneticsensitivity direction of the sensor becomes longer. Accordingly, theshape magnetic anisotropy in the end portions 1 has an easy axis in thetransverse direction of the sensor. As a consequence, the flux densityof the end portions 1 tends to become more sensitive to the magneticfield in an orthogonal direction relative to the magnetic sensitivitydirection of the sensor. As a result, if an electronic compass iscreated by arranging a plurality of the above described fluxgate sensorsperpendicularly to each other, the magnetic cores of the fluxgatesensors are easily affected by the magnetic field in an orthogonaldirection relative to the detection magnetic field, and the cross-axissensitivity of the electronic compass increases. Moreover, because adistortion is generated in the pickup waveform by the magnetic field inan orthogonal direction relative to the detection magnetic field, outputabnormalities are easily generated and the orthogonality of each axisdeteriorates. Here, the term cross-axis sensitivity refers to changes inthe output of the magnetic field in the X-axial direction in a sensorwhose magnetic sensitivity direction is the Y-axial direction or theZ-axial direction when, for example, the magnetic field in the X-axialdirection is being detected. If the cross-axis sensitivity increases,the orthogonality of the axes deteriorates, and the azimuth accuracy ofthe electronic compass also deteriorates. In addition, not only arepulse-shaped temporal changes in the pickup voltage included in thecross-axis sensitivity, but changes in output that are caused by changesin the pulse waveform itself are also included therein.

SUMMARY

The present invention provides a fluxgate sensor that, in addition tohaving a small size and a high level of sensitivity, has a high level ofexcitation efficiency, and a high degree of design freedom, and alsoprovides an electronic compass in which this fluxgate sensor is used.

The fluxgate sensor of the present invention includes: a first wiringlayer that is formed on a substrate; a first insulating layer that isformed so as to cover the first wiring layer; a magnetic core that isformed on the first insulating layer, and that includes a centerportion, and first and second end portions that are continuous with thecenter portion and have a broader width than the width of the centerportion, and are positioned at the two ends of the center portion; asecond insulating layer that covers the magnetic core, and is formed onthe first insulating layer; and a second wiring layer that is formed onthe second insulating layer, and it is also possible for the firstwiring layer and the second wiring layer to have a plurality of wiresthat are substantially parallel to each other, and for the two ends ofthe wires of the first wiring layer and of the wires of the secondwiring layer to be electrically connected together via portions wherethe first insulating layer and the second insulating layer have beenselectively removed, and for spiral-shaped first solenoid coils to bewound around the first and second end portions, and for a spiral-shapedsecond solenoid coil to be wound around the center portion.

It is also possible for the first solenoid coil to contain a thirdsolenoid that is wound around the first end portion and a fourthsolenoid coil that is wound around the second end portion, and for thethird solenoid coil and the fourth solenoid coil to be connectedtogether in series, and have substantially the same number of winds. Itis desirable for the third solenoid coil and the fourth solenoid coil tohave the same number of winds, however, due to factors such as the wayin which the electrode pads are wound, cases in which the number ofwinds are not absolutely identical are also acceptable.

It is also possible for the first solenoid coil to be wound around thecenter portion and the first and second end portions.

It is also possible for a value of a ratio B/D between a width B of thefirst and second end portions and a length D of the longitudinaldirection of the first and second end portions to be less than 1.

The electronic compass of the present invention includes: a substrate;and first, second, and third fluxgate sensors that are located on thesubstrate, and that are aligned respectively with three axes, and eachof the first, second, and third fluxgate sensors includes: a firstwiring layer that is formed on a substrate; a first insulating layerthat is formed so as to cover the first wiring layer; a magnetic corethat is formed on the first insulating layer, and that includes a centerportion, and first and second end portions that are continuous with thecenter portion and have a broader width than the width of the centerportion, and are positioned at the two ends of the center portion; asecond insulating layer that covers the magnetic core, and is formed onthe first insulating layer; and a second wiring layer that is formed onthe second insulating layer, and it is also possible for the firstwiring layer and the second wiring layer to have a plurality of wiresthat are substantially parallel to each other, and for the two ends ofthe wires of the first wiring layer and of the wires of the secondwiring layer to be electrically connected together via portions wherethe first insulating layer and the second insulating layer have beenselectively removed, and for spiral-shaped first solenoid coils to bewound around the first and second end portions, and for a spiral-shapedsecond solenoid coil to be wound around the center portion.

It is also possible for the first solenoid coil to contain a thirdsolenoid that is wound around the first end portion and a fourthsolenoid coil that is wound around the second end portion, and for thethird solenoid coil and the fourth solenoid coil to be connectedtogether in series, and have substantially the same number of winds.

It is also possible for the first solenoid coil to be wound around thecenter portion and the first and second end portions.

It is also possible for a value of a ratio B/D between a width B of thefirst and second end portions and a length D of the longitudinaldirection of the first and second end portions to be less than 1.

The fluxgate sensor of the present invention includes at least: a firstwiring layer; a first insulating layer that is formed so as to cover thefirst wiring layer; a magnetic core that is formed on the firstinsulating layer, and that is provided with a detection portion, andfirst and second excitation portions that are continuous with thedetection portion and have a broader width than the width of thedetection portion, and are positioned at the two ends of the detectionportion; a second insulating layer that covers the magnetic core, and isformed on the first insulating layer; and a second wiring layer that isformed on the second insulating layer, and it is also possible for thefirst wiring layer and the second wiring layer to have a plurality ofwires that are substantially parallel to each other, and for the twoends of the wires of the first wiring layer and of the wires of thesecond wiring layer to be electrically connected together via portionswhere the first insulating layer and the second insulating layer havebeen selectively removed, and for spiral-shaped excitation coils to bewound around the first and second excitation portions.

It is also possible for the excitation coils to contain a firstexcitation coil that is wound around the first excitation portion, and asecond excitation coil that is wound around the second excitationportion, and for the first excitation coil and the second excitationcoil to be connected together in series such that the magnetic fieldsthey generate are aligned in the same direction.

It is also possible for the excitation coils to be wound around theexcitation portions and the detection portion that is formed in thecenter portion of the magnetic core.

It is also possible for an electronic compass of the present inventionto be formed such that three fluxgate sensors are located on a singlesubstrate, so that they are aligned respectively with three axes.

According to the present invention, by winding excitation coils aroundthe wide end portions of a magnetic core, the number of coils wound onthe excitation coil is increased, and magnetic flux generated from theexcitation coils in the end portions can be applied in concentration inthe center portion.

According to the present invention, because it is possible to supplycurrent simultaneously to two excitation coils, the electrode pads canbe decreased, and a reduction in size can be achieved.

According to the present invention, by winding an excitation coil in acenter portion as well, even stronger excitation can be performed.

According to the present invention, by using a highly accurate fluxgatesensor, the high level of azimuth accuracy can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing an example in which the shape of endportions of a magnetic core of a fluxgate sensor according to a firstpreferred embodiment of the present invention is rectangular.

FIG. 1B is a plan view showing an example in which boundary portionsbetween end portions 1 and a center portion 2 of the magnetic core ofthe fluxgate sensor according to the first preferred embodiment of thepresent invention are tapered.

FIG. 2 contains graphs (a)-(c) showing an operating principle of thefluxgate sensor according to the first preferred embodiment of thepresent invention.

FIG. 3 is a hysteresis loop showing changes over time in themagnetization state of the magnetic core of the fluxgate sensoraccording to the first preferred embodiment of the present invention.

FIG. 4 is a top view schematically showing the fluxgate sensor accordingto the first preferred embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along a line a-a′ shown in FIG.4.

FIG. 6A is a cross-sectional view taken along a line b-b′ shown in FIG.4, and shows a fluxgate sensor manufacturing step.

FIG. 6B is a cross-sectional view taken along a line b-b′ shown in FIG.4, and shows a fluxgate sensor manufacturing step.

FIG. 6C is a cross-sectional view taken along a line b-b′ shown in FIG.4, and shows a fluxgate sensor manufacturing step.

FIG. 6D is a cross-sectional view taken along a line b-b′ shown in FIG.4, and shows a fluxgate sensor manufacturing step.

FIG. 6E is a cross-sectional view taken along a line b-b′ shown in FIG.4, and shows a fluxgate sensor manufacturing step.

FIG. 7A is a view illustrating an example of the shape of the magneticcore of the fluxgate sensor according to the first preferred embodimentof the present invention.

FIG. 7B is a view illustrating an example of the shape of the magneticcore of the fluxgate sensor according to the first preferred embodimentof the present invention.

FIG. 7C is a view illustrating an example of the shape of the magneticcore of the fluxgate sensor according to the first preferred embodimentof the present invention.

FIG. 8 is a schematic perspective view of an electronic compassaccording to a first preferred embodiment of the present invention.

FIG. 9 is a graph showing a pickup voltage waveform of the fluxgatesensor according to the first preferred embodiment of the presentinvention.

FIG. 10 is a graph showing the external magnetic field dependence of theoutput of the fluxgate sensor according to the first preferredembodiment of the present invention.

FIG. 11 is a graph showing the results when the magnetic flux densityinside the core in the fluxgate sensor according to the first preferredembodiment of the present invention was calculated.

FIG. 12 is a view illustrating how excitation coils and a detection coilare wound in a fluxgate sensor according to a second preferredembodiment of the present invention.

FIG. 13 contains graphs showing pickup voltage waveforms relative to amagnetic field that is orthogonal to the direction of magneticsensitivity in the fluxgate sensor of a comparative example.

FIG. 14 contains graphs showing pickup voltage waveforms relative to amagnetic field that is orthogonal to the direction of magneticsensitivity in the fluxgate sensor of an example of the presentinvention.

FIG. 15 is a schematic view showing the shape of a magnetic core in aconventional fluxgate sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teaching ofthe present invention and that the present invention is not limited tothe embodiments illustrated for explanatory purpose.

First Preferred Embodiment

Hereinafter, a first preferred embodiment of the present invention willbe described in detail with reference made to the drawings.

FIG. 1A and FIG. 1B are plan views showing examples of the shape of amagnetic core of a fluxgate sensor according to a first preferredembodiment of the present invention. As is shown in FIG. 1A and FIG. 1B,the magnetic core of the fluxgate sensor of the first preferredembodiment of the present invention has end portions 1 and a centerportion 2. A width B of the end portions 1 is greater than a width C ofthe center portion 2. A length A in the longitudinal direction of themagnetic core is not more than 1 mm, and desirably not more than 0.5 mm.The value of a ratio B/D between the width B of the end portions 1 and alength D in the longitudinal direction of the end portions 1 is lessthan 1. The longitudinal direction of the magnetic core of the fluxgatesensor coincides with the direction of magnetic sensitivity of thefluxgate sensor. Although not shown in FIGS. 1A and 1B, excitation coilsare wound around the circumferences of the end portions 1, and a pickupcoil is wound around the circumference of the center portion 2. FIG. 1Ais a plan view showing an example in which the shape of the end portionsof the magnetic core is rectangular. FIG. 1B is a plan view showing anexample in which boundary portions between the end portions 1 and thecenter portion 2 of the magnetic core have a tapered shape. As is shownin FIG. 1B, in order to suppress localized saturation of the magneticflux in corner portions, it is desirable for the boundary portionsbetween the end portions 1 and the center portion 2 to be asubstantially tapered shape. In this case, if the length D in thelongitudinal direction of the end portions 1 represents a length whichincludes the substantially tapered portion, then it is desirable for thevalue of the ratio B/D between the width B of the end portions 1 and thelength D in the longitudinal direction of the end portions 1 to be lessthan 1.

In a magnetic thin-film the ratio between the film-thickness directionand the in-plane direction is sizable at between several hundreds andseveral thousands. Accordingly, there is a difference in thedemagnetization field coefficients of between several hundreds andseveral thousands between the film-thickness direction and the in-planedirection, so that the demagnetization field coefficient in the in-planedirection is extremely small. If the magnetic thin-film is patterned soas to provide it with a longitudinal direction, then the demagnetizationfield coefficient is decided by the dimensional ratio between thelongitudinal direction and the transverse direction. In this case, thereis a small demagnetization field coefficient in the longitudinaldirection, and a large demagnetization field coefficient in thetransverse direction. Consequently, the shape anisotropy is such thatthe easy axis is in the longitudinal direction.

As is described above, the fluxgate sensor of the first preferredembodiment of the present invention has the end portions 1 which arewider than the center portion 2 in the magnetic core thereof, and thewidth B of the end portions 1 is smaller than the length D in thelongitudinal direction of the end portions 1. The easy axis according tothe shape anisotropy of the end portions 1 is the longitudinal directionof the fluxgate sensor. Accordingly, there is little change in the fluxdensity within the core that is caused by the magnetic field which isorthogonal to the direction of magnetic sensitivity, so that thesensitivity characteristics of the other axes are excellent. As aconsequence, it is possible to create an electronic compass that hassuperior azimuth accuracy.

Operating principles of the fluxgate sensor according to the firstpreferred embodiment of the present invention will now be described.

FIG. 2 contains graphs that show the operating principles of thefluxgate sensor according to the first preferred embodiment of thepresent invention. FIG. 2( a) is a graph that shows changes over time ina triangular wave current which is supplied to an excitation coil. FIG.2( b) is a graph that shows changes over time in the magnetization stateof a core. FIG. 2( c) is a graph that shows changes over time in theoutput voltage generated in a pickup coil. FIG. 3 is a hysteresis loopshowing changes over time in the magnetization state of the magneticcore of the fluxgate sensor according to the first preferred embodimentof the present invention. When a triangular wave current such as thatshown in FIG. 2( a) is supplied to the excitation coil, the magneticcore is excited by a magnetic field Hexc created by the excitation coil,and because the flux density B within the magnetic core, namely, themagnetization state of the magnetic core has saturation characteristics,it changes over time in the manner shown in FIG. 2( b). In areas in thepickup coil where a time derivative of the flux density B of themagnetic core, namely, where the temporal change dB/dt is present, anoutput voltage Vpu=NS×dB/dt which is proportional to the cross-sectionalarea S of the magnetic core and the number of winds N in the pickup coilis generated. The output voltage Vpu of the pickup coil changes overtime in the manner shown in FIG. 2( c). The greater the size of thetemporal change dB/dt of the flux density B of the magnetic core, thehigher the high value of the pickup voltage wave and the narrower thepulse width, so that a steeper pulse voltage is obtained. A timeinterval t1 shown in FIG. 2( c) is expressed by the following Formula(1) using an external magnetic field Hext, a shift Hc in the strength Hof the magnetic field between when flux density B of the magnetic coreincreases and when it decreases, the magnetic field Hexc created by theexcitation coil, a period T of the triangular wave, and a delay time Tdcreated by the inductance of the coil.

$\begin{matrix}{t_{1} = {{\left( \frac{H_{exc} + H_{c} - H_{ext}}{H_{exc}} \right)\frac{T}{4}} + T_{d}}} & (1)\end{matrix}$

In the same way, a time interval t2 shown in FIG. 2( c) is expressed bythe following Formula (2).

$\begin{matrix}{t_{2} = {{\left( \frac{H_{exc} + H_{c} - H_{ext}}{H_{exc}} \right)\frac{T}{4}} + T_{d}}} & (2)\end{matrix}$

An amount of change t2−t1 in the time interval relative to the externalmagnetic field obtained from Formula (1) and Formula (2) is expressed bythe following Formula (3).

$\begin{matrix}{{t_{2} - t_{1}} = {\frac{H_{ext}}{H_{exc}}\frac{T}{2}}} & (3)\end{matrix}$

From Formula (3) it can be seen that the amount of change t2−t1 in thetime interval relative to the external magnetic field depends on theratio Hext/Hexc between the external magnetic field Hext and themagnetic field Hexc created by the excitation coil, and on the period Tof the triangular wave. The sensitivity S=d (t2−t1)/d Hext relative tothe external magnetic field is expressed by S=T/(2·Iexc×α) using theamplitude Iexc of the current supplied to the excitation coil, thegenerated magnetic field per unit of current flowing in the excitationcoil, namely, the excitation efficiency α, and the period T of thetriangular wave. Accordingly, the greater the excitation current, thesmaller the sensitivity S of the sensor. The greater the period T of thetriangular wave, namely, the smaller the excitation frequency fexc, thegreater the sensitivity S of the sensor.

The excitation efficiency a is a value which is determined by the numberof winds of the coil and the magnetic core which make up the fluxgatesensor. The greater the excitation efficiency α, the smaller the currentrequired to drive the fluxgate sensor. Moreover, in Formula (3), Formula(3) is 0 when Hext=Hexc, and at this time, Hext forms the upper limit ofthe measured magnetic field range. Because Hexc is expressed as=α×Iexc,the greater the excitation efficiency α, the broader the measuredmagnetic field range becomes if the fluxgate sensor is driven by thesame current.

FIG. 4 is a top view schematically showing the fluxgate sensor accordingto the first preferred embodiment of the present invention. FIG. 5 is across-sectional view taken along a line a-a′ shown in FIG. 4. FIGS. 6Athrough 6E are cross-sectional views taken along a line b-b′ shown inFIG. 4, and show fluxgate sensor manufacturing steps.

As is shown in FIG. 4 and FIG. 5, the fluxgate sensor of the firstpreferred embodiment of the present invention includes a magnetic core3, a first wiring layer 4, a first insulating layer 5, a secondinsulating layer 6, a second wiring layer 7, an aperture portion 8, anda substrate 100. The magnetic core 3 includes end portions 1 and acenter portion 2. The first wiring layer 4 and the second wiring layer 7form first solenoid coils 9 which are wound around the end portions 1,and a second solenoid coil 10 which is wound around the center portion2.

In the first preferred embodiment of the present invention, the firstsolenoid coils 9 which are wound around the end portions 1 formexcitation coils. The second solenoid coil 10 which is wound around thecenter portion 2 forms a pickup coil. In the first preferred embodimentof the present invention the end portions 1 form excitation portions,and the center portion 2 forms a detection portion.

A process to manufacture the fluxgate sensor of the first preferredembodiment of the present invention will now be described using FIGS. 6Athrough 6E. Firstly, as is shown in FIG. 6A, the first wiring layer 4which is used to form the bottom-side wiring of the solenoid coils isformed on the non-magnetic substrate 100. Next, as is shown in FIG. 6B,the first insulating layer 5 which is used to insulate the magnetic core3 and the solenoid coil is formed on the first wiring layer 4. Here, theaperture portions 8 are formed in those portions of the first insulatinglayer 5 where the first wiring layer 4 and the second wiring layer 7,which forms the top-side wiring of the solenoid coil which is formedsubsequently, are connected together.

Next, as is shown in FIG. 6C, the magnetic core 3 which is formed by asoft magnetic body film is formed on the first insulating layer 5. As isshown in FIG. 4, the shape of this magnetic core 3 which is formed froma soft magnetic body film is such that the width of the center portion 2is narrower than the width of the end portions 1.

Next, as is shown in FIG. 6D, the second insulating layer 6 in which theaperture portions 8 are provided in connecting portions between thefirst wiring layer 4 and the second wiring layer 7 is formed on top ofthe magnetic core 3. Furthermore, as is shown in FIG. 6E, the secondwiring layer 7 is formed on top of the second insulating layer 6 suchthat the end portions of the wires thereof are connected to the endportions of the wires of the first wiring layer 4 which are adjacentthereto, so as to thereby form a solenoid coil. Because the wires areconnected to the wires which are adjacent thereto, the loop of thesolenoid coil as seen in cross-section is not closed.

The first solenoid coils 9 and the second solenoid coil 10 which areformed by the first wiring layer 4 and the second wiring layer 7 arewound independently of each other in the wide end portions 1 at bothends of the magnetic core 3, and in the narrow center portion 2 thereof.The first solenoid coils 9 which are around the wide end portions 1 atthe two ends of the magnetic core 3 include a third solenoid coil whichis wound around the end portion 1 at one end thereof, and a fourthsolenoid coil which is wound around the end portion 1 at the other endthereof. The third solenoid coil and the fourth solenoid coil at the twoend portions are connected together in series by the first wiring layer4 or the second wiring layer 7 such that the directions of the magneticfields they generate are the same, and such that together they form thefirst solenoid coils 9. Electrode pads 11 which are used for externalconnections are formed at both ends of the second solenoid coil 10 whichis wound around the center portion 2 of the magnetic core 3. Electrodepads 12 which are used for external connections are formed at both endsof the two first solenoid coils 9 which are wound around the endportions 1 at both ends of the magnetic core 3 and are connectedtogether in series.

It is preferable for the third solenoid coil and the fourth solenoidcoil that are wound respectively around the two end portions of themagnetic core 3 to have the same number of winds and to be mutuallysymmetrical.

Note that a portion of the bottom-side wiring of the magnetic core 3 inwhich the first solenoid coil 9 and the second solenoid coil 10 areshown in typical form has been omitted from FIG. 4. Moreover, the shapeof the first solenoid coil 9 and the second solenoid coil 10 is notlimited to the shape shown in FIG. 4.

FIG. 5 is an example of a cross-sectional view taken along a line a-a′shown in FIG. 4 of the fluxgate sensor according to the first preferredembodiment of the present invention, and the positional relationshipbetween the first wiring layer 4 and the second wiring layer 7 in thefluxgate sensor according to the first preferred embodiment of thepresent invention is not limited to the configuration shown in FIG. 5.

FIGS. 6A through 6E are examples of a cross-sectional view taken along aline b-b′ shown in FIG. 4 of the fluxgate sensor according to the firstpreferred embodiment of the present invention, and the shape of thefluxgate sensor according to the first preferred embodiment of thepresent invention is not limited to the shape shown in FIGS. 6A through6E.

The wide end portions 1 at both ends of the magnetic core 3 are excitedas a result of power being supplied to the first solenoid coils 9 whichare wound around the circumferences thereof. In contrast, inducedvoltage is applied to the narrow center portion 2 of the magnetic core3, and this induced voltage is detected by the second solenoid coil 10which is wound around the circumference of the center portion 2.

Alternating current which changes over time is supplied from the outsidevia the electrode pads 12 to the first solenoid coils (i.e., theexcitation coils) 9 at the end portions 1 of the magnetic core 3,resulting in the magnetic core 3 undergoing alternating excitation. Themagnetic flux generated in the end portions 1 is guided to the centerportion 2 of the magnetic core 3. As a result of this, the centerportion 2 of the magnetic core 3 also undergoes alternating excitation,and a substantially pulse-shaped induced voltage is generated in thesecond solenoid coil (i.e., the detection coil) 10 of the center portion2. This induced voltage can be detected by the second solenoid coil 10and by an external detection circuit via the electrode pads 11. Here, itis desirable for the alternating current which is supplied to the firstsolenoid coil 9 to be a fixed frequency triangular wave.

At this time, if an external magnetic field is applied, the timings atwhich the aforementioned substantially pulse-shaped induced voltage isgenerated show changes over time. A positive induced voltage is outputat the timings when the triangular wave current switches from positiveto negative. Moreover, a negative induced voltage is output at thetimings when the triangular wave current switches from negative topositive. Accordingly, by measuring with a counter the timings at whichthese positive-negative pulse-shaped induced voltages are generated, itis possible to obtain responses to the external magnetic field.

Note that in the above described first preferred embodiment, themagnetic core shown in FIG. 4 is used as an example of a magnetic core,however, as far as the purpose of the present invention is concerned,the shape of the magnetic core is not limited to this shape and anyshape may be employed provided that the width of the end portionsthereof is wider than the width in the center portion thereof. FIGS. 7Athrough 7C illustrate examples of shapes of the magnetic core of thefluxgate sensor according to the first preferred embodiment of thepresent invention. Note that in FIGS. 7A through 7C which are typicalviews, the magnetic core and the top-side wiring of the first solenoidcoil 9 and the second solenoid coil 10 are shown, while, in actual fact,when viewed from above the drawing, portions of the magnetic core thatoverlap the coils are hidden by the coils.

In addition to the above described structure, it is also possible for asealing layer to be formed covering the second wiring layer 7 as part ofthe structure of the fluxgate sensor.

Next, a method of manufacturing the fluxgate sensor according to thefirst preferred embodiment of the present invention will be described.

Firstly, a film of a barrier metal such as Ti, Cr, TiW or the like isformed on top of the non-magnetic substrate 100 by sputtering, and afilm of Cu is then formed on top of this by sputtering. Next, a resistpattern which will become the first wiring layer 4 is formed by means ofphotolithography, and the wiring pattern is then formed by wet etching.Alternatively, it is also possible to form the first wiring layer 4 bymeans of electroplating using the aforementioned sputtered films as seedfilms. At this time, in order to form the magnetic core 3 of top of theinsulating layer which is formed after this, it is desirable for thethickness of the first wiring layer 4 to be such that bumps andindentations in the surface of the insulating layer created by thiswiring are sufficiently small compared to the thickness of the magneticcore, and such that the resistance of the coil is low. Specifically, itis preferable for the thickness of the first wiring layer 4 to bebetween 0.2 μm and 2 μm.

Next, the first insulating layer 5 is formed by coating a photosensitiveresin thereon and then performing exposure, developing, andthermosetting processing. At this time, portions where the first wiringlayer 4 and the second wiring layer 7 which is formed subsequently areconnected together are left open, and the first wiring layer 4 and themagnetic core 3 which is formed subsequently are insulated from eachother. At this time, it is desirable for the thickness of the firstinsulating layer 5 to only be sufficiently thick to soften any bumps andindentations in the first wiring layer 4. Specifically, it is desirablefor the thickness of the first insulating layer 5 to be approximately 3to 10 times the thickness of the first wiring layer 4. Note that, inFIG. 5, in order for the first wiring layer 4 to be displayed at asuitable size in the drawing, the respective layers are not shown inthese proportions.

Moreover, at this time, photosensitive polyimide is required in order toprotect against any distortion being generated in the magnetic core 3which is due to contraction and deformation caused by heat history inthe subsequent steps. Consequently, it is desirable for thephotosensitive polyimide to be a resin which has a sufficient heatresistance so that thermal contraction and deformation which are caused,for example, by solder reflow during packaging and by the thermalprocessing in the magnetic field which is performed in order to impartinduced magnetic anisotropy to the magnetic core do not occur.Specifically, it is desirable for the glass transition temperature (Tg)of the photosensitive polyimide to be not less than 300° C. Namely, itis desirable for the resin which is used here to be a polyimide orpolybenzoxazole having high heat resistance, or a thermally curednovolac-based resin.

Next, the soft magnetic body film which forms the magnetic core 3 isformed by sputtering, and patterning is then performed thereon viaphotolithography and etching such that the desired shape is achieved.For the soft magnetic body film, zero magnetostriction Co-basedamorphous films which are typified by CoNbZr and CoTaZr and the like, aswell as NiFe alloys, and CoFe alloys and the like are desirably used.Because these soft magnetic body films are difficult materials to etch,it is also possible to perform the sputtering film formation afterfirstly forming a resist layer, and then using a photolithographicmethod to remove the resist so as to obtain the desired pattern.Moreover, after the magnetic film which will form the magnetic core 3has been formed, it is desirable to perform heat processing in arotating magnetic field or heat processing in a static magnetic field inorder to remove stress and non-uniform uniaxial anisotropy which isimparted thereto during film formation, and to impart uniform inducedmagnetic anisotropy.

Moreover, it is also possible to form the magnetic core 3 by molding aNiFe alloy or a CoFe alloy into a desired shape using an electroplatingmethod which employs a resist frame.

Next, the second insulating layer 6 is formed by performing exposure,developing, and thermosetting processing on the photosensitive resinsuch that the connecting portions between the first wiring layer 4 andthe second wiring layer 7 are left open, and such that the magnetic core3 and the second wiring layer 7 are electrically insulated from eachother.

Next, a seed film is formed by firstly forming a film of a barrier metalsuch as Ti, Cr, TiW or the like by means of sputtering on the substrateincluding the second insulating layer 6 and the aperture portions in thesecond insulating layer 6, and by then forming a film of Cu thereon bymeans of sputtering. Next, a resist frame is formed and a desired wiringpattern is formed by Cu electroplating. This seed layer is then etchedso as to form the second wiring layer 7.

Finally, by forming electrode pads and terminals which are used to makeexternal connections, as well as a protective film where these arenecessary, the fluxgate sensor according to the first preferredembodiment of the present invention is created. Here, it is possible toapply methods which are used for typical semiconductor devices andthin-film devices such as sold bumps, metal bumps, and wire bonding andthe like to the forming of the externally connected terminals.

Note that, in the above description, sputtered and electroplated Cu isused for the first wiring layer 4 and the second wiring layer 7,however, these may also be formed using electroless Cu or electrolyticAu plating, and it is also possible to use a superconductive film whichis formed by a sputtered film of Cu, Al, or Au or the like. In addition,a resin material is used for the first insulating layer 5 and the secondinsulating layer 6, however, it is also possible to form an insulatingfilm of SiO2, SiN, Al2O3 or the like by sputtering or chemical vapordeposition (CVD), and to form the above described aperture portions bymeans of dry etching.

Next, an electronic compass of the first preferred embodiment of thepresent invention will be described. FIG. 8 is a schematic perspectiveview showing an electronic compass according to the first preferredembodiment of the present invention.

The electronic compass shown in FIG. 8 is formed by mounting a firstfluxgate (X-axis) sensor 20, a second fluxgate (Y-axis) sensor 30, athird fluxgate (Z-axis) sensor 40, and an IC 50 for signal processing ona single substrate. Specifically, the first fluxgate sensor 20 and thesecond fluxgate sensor 30 are positioned such that their formed surfacesare substantially parallel to the surface of the substrate used to formthe electronic compass, and such that their directions of magneticsensitivity are orthogonal to each other. The fourth fluxgate sensor 40is positioned so as to be substantially perpendicular to the surface ofthe substrate used to form the electronic compass. At this time, in thefirst fluxgate sensor 20, the second fluxgate sensor 30, and the thirdfluxgate sensor 40, it is desirable for the shapes of all areasexcluding the external connection terminals, namely, for the shapes ofthe portions where the magnetic core 3 and the coils 61 and 71 areformed to be the same. The reason for this is that, by making thecharacteristics of each of the first fluxgate sensor 20, the secondfluxgate sensor 30, and the third fluxgate sensor 40 all uniform, thereis no need to correct any variations in the characteristics of eachsensor, and it becomes possible to simplify the electronic circuitry.Moreover, because the third fluxgate sensor 40 is mounted substantiallyperpendicular relative to the substrate surface, it is desirable for thelength of the direction of magnetic sensitivity thereof to be 1 mm orless, and more preferably to be approximately 0.5 mm in order to reducethe thickness of the electronic compass.

The signal processing IC 50 is provided with a circuit that suppliestriangular wave current of a fixed frequency to the excitation coil 61in each fluxgate sensor, a detection circuit that is used to detect theinduced voltage appearing in the detection coil 71, a counter that isused to count the timings at which the induced voltage is generated, anda selector that is used to switch the connections with theaforementioned two circuits between the first fluxgate sensor 20, thesecond fluxgate sensor 30, and the third fluxgate sensor 40. Byemploying this structure, it is possible to sequentially measure therespective magnetic fields in three axial directions by means of thefirst fluxgate sensor 20, the second fluxgate sensor 30, and the thirdfluxgate sensor 40, and, by making calculations, to obtain an electroniccompass having minimal bearing errors.

EXAMPLES

A fluxgate sensor was manufactured in the above described manner for useas an example. The shape of the magnetic core of the fluxgate sensor wasas follows: the length A in the longitudinal direction of the magneticcore=480 μm, the width B of the end portions 1=80 μm, the width C of thecenter portion 2=20 μm, the length D in the longitudinal direction ofthe end portions 1=140 μm, the number of winds in the excitation coilswas 16.5, and the number of winds in the pickup coil was 6.5.

FIG. 9 is a graph showing the output waveform of a positive/negativepulse-shaped pickup voltage when a triangular wave current having anamplitude of 100 mA, and a frequency of 30 kHz was supplied to thefluxgate sensor of the aforementioned example. FIG. 10 is a graphshowing the output from a fluxgate sensor relative to the externalmagnetic field dependency, namely, the external magnetic field in a timeinterval t during which the positive/negative pulse-shaped pickupvoltage shown in FIG. 9 exceeded the respective reference voltages Vth.

It is possible to improve the number of winds on the excitation coils bywinding solenoid coils around the wide end portions 1 of the magneticcore of the fluxgate sensor.

By doing this, even if the size of the sensor is miniaturized to 0.5 mmor less, a pickup waveform having a superior SN ratio can be obtained.The output of the fluxgate sensor of the above described exampleexhibited excellent linearity even relative to an external magneticfield, and any shift from an ideal straight line was 0.5% within a rangeof ±14 Oe. The excitation efficiency a of the above described fluxgatesensor was 0.29 Oe/mA.

As a comparative example, a fluxgate sensor shown in FIG. 15 having thesame sensor length as the fluxgate sensor of the above describedexample, and in which the coils were wound at the same wiring pitcheswas manufactured. The fluxgate sensor of this comparative example had acore in which the length A in the longitudinal direction of the magneticcore=480 μm, the width B of the end portions 1=600 μm, the width C ofthe center portion 2=30 μm, and the length D in the longitudinaldirection of the end portions 1=60 μm. In the fluxgate sensor of thiscomparative example, the excitation efficiency was 0.20 Oe/mA.Accordingly, it is clear that the fluxgate sensor according to theexample of the present invention has a high level of excitationefficiency.

The fluxgate sensor of the first preferred embodiment of the presentinvention has a structure in which solenoid coils are wound as far asthe ends of the end portions 1, and because there are a large number ofwinds in the solenoid coils, and because the width of the end portions 1is greater than the width of the center portion 2, magnetic fluxgenerated in the end portions 1 becomes concentrated in the centerportion 2. Accordingly, the magnetic flux density of the center portion2 is greater than the magnetic flux density of the end portions 1, andthe apparent value of the magnetic field Hexc created by the excitationcoils in the center portion 2 increases. As a result of this, thefluxgate sensor according to the first preferred embodiment of thepresent invention has a high level of excitation efficiency.

FIG. 11 is a graph showing the results when the magnetic flux density ata cross-section a-a′ of the core interior when excitation current wassupplied to the fluxgate sensor according to the first preferredembodiment of the present invention shown in FIG. 4 were calculatedusing a three-dimensional finite element method. Because a structure inwhich the width B of the end portions 1 is larger than the width C ofthe center portion 2 is employed in the magnetic core of the fluxgatesensor, it can be seen from FIG. 11 that the magnetic flux density ofthe center portion 2 is higher than the magnetic flux density of the endportions 1, and that the magnetic flux density of the center portion 2becomes saturated by a smaller current value. This fact shows that, inthe fluxgate sensor according to the first preferred embodiment of thepresent invention, the apparent magnetic field Hexc created by theexcitation coil increases, and the excitation efficiency increases.

As has been described above, in the first preferred embodiment of thepresent invention, in a fluxgate sensor that is formed by a thin film,it is possible to reduce the diamagnetic field of a detection portion byusing an H-type magnetic core to compensate for any reduction insensitivity which is caused by the diamagnetic field when the fluxgatesensor is reduced in size. By doing this, even though the size has beenreduced, the excitation efficiency is increased, and it is possible toconstruct a highly sensitive fluxgate sensor. It is also possible toconstruct a fluxgate sensor that has high sensitivity at a lower currentand has a wide measurement magnetic field range.

As has been described above, in the first preferred embodiment of thepresent invention, excitation coils are wound onto the broad-width endportions 1 at the two ends of an H-type magnetic core. The magnetic fluxgenerated in this magnetic core by the excitation coils is expressed bythe cross-sectional area of the broad-width end portions 1 at both endsof the magnetic core x the magnetic flux density. When alternatingcurrent is supplied to the excitation coils, the magnetic flux generatedin the magnetic core by the excitation coils is guided to thenarrow-width center portion 2 of the magnetic core which is continuouswith the end portions of the magnetic core. At this time, using thewidth B of the end portions 1 of the magnetic core and the width C ofthe center portion 2 thereof, the cross-sectional area of the centerportion 1 is C/B times the cross-sectional area of the broad-width endportions 1 at the two ends. In the process whereby the magnetic flux isguided from the end portions 1 at the two ends of the magnetic core tothe center portion 2 thereof, then unless there is any magnetic fluxloss, the magnetic flux is the same in the end portions 1 and the centerportion 2. Consequently, the magnetic flux density of the center portion2 is B/C times the magnetic flux density of the end portions 1.Accordingly, the greater the ratio between the widths of the endportions 1 of the magnetic core and the center portion 2 thereof, themore the magnetic flux density improves markedly.

As has been described above, in the first preferred embodiment of thepresent invention, the excitation coils and the detection coil are woundindependently of each other. As a result, it is possible to set optionalvalues for the number of winds on the excitation coils and the detectioncoil, the wire width, and the space between the wires. Consequently, theexcitation coils and the detection coil can be freely designed to matchthe specifications sought in the sensor.

As has been described above, in the first preferred embodiment of thepresent invention, solenoid coils are wound over the entire area of themagnetic core. Accordingly, compared with the structures described inJapanese Unexamined Patent Application, First Publication No.2007-279029 and PCT International Publication No. WO 2007-126164Pamphlet, it is possible for the number of winds in the solenoid coilsto be increased, and for the magnetic flux generated in the magneticcore to be increased. Consequently, the magnetic flux density in thecenter portion 2 is raised, and the detection sensitivity of themagnetic sensor is improved.

When the width of the portions connecting together the end portions 1 atboth ends of the magnetic core with the center portion 2 thereof becomesabruptly narrower at an angle which is close to a right angle, as isshown in FIG. 1A, because localized magnetic flux saturation tends tooccur in these angle portions, there is a possibility of magnetic fluxloss occurring. In contrast, as is shown in FIG. 1B, if a tapered shapeis provided at the boundary portions between the end portions 1 of themagnetic core and the center portion 2 thereof, then it is possible tosuppress localized magnetic flux saturation, and the magnetic fluxdensity in the center portion 2 of the magnetic core can be improved.

The cross-axis sensitivity will now be described. FIG. 13 containsgraphs showing pickup voltage waveforms relative to a magnetic fieldthat is orthogonal to the direction of magnetic sensitivity whenmagnetic fields of 0 Oe through 10 Oe are applied in orthogonaldirections within the film plane in the fluxgate sensor of the abovedescribed comparative example. From FIG. 13 it can be understood that byapplying a magnetic field which is orthogonal to the direction ofmagnetic sensitivity, the timings at which a pickup voltage is generatedas well as the peak height of the pickup voltage both change, andcross-axis sensitivity is generated. It can also be seen that thechanges caused by an external magnetic field of approximately 4 Oethrough 6 Oe are particularly conspicuous. Even when thesecharacteristics were obtained for a magnetic field which is orthogonalto the direction of magnetic sensitivity of the sensor, then if onlygeomagnetism of approximately 0.3 Oe is being detected, the effect onthe azimuth accuracy is small. However, if the sensor is actuallymounted on an electronic instrument and used, the magnetic fieldgenerated from the components mounted inside the instrument becomesadded to this. Consequently, in some cases the magnetic field generatedfrom the components mounted inside the instrument creates offset fromthe geomagnetism, and it is no longer possible to obtain accuratemeasurements. Accordingly, it becomes necessary to measure and calculatethe offset magnetic field generated from peripherally mountedcomponents, and then perform calibration in order to measure thegeomagnetism. However, as is described above, if the sensor has thecharacteristic that its output varies relative to a magnetic field in anorthogonal direction relative to the direction of magnetic sensitivityof the sensor, then if the offset magnetic field is overlapped in anorthogonal direction relative to the sensor, not only does the size ofthe error in the value itself which was calculated for the offsetmagnetic field increase, but because the output is changed by theoverlapping of the offset magnetic field, there is a deterioration inthe geomagnetism detection accuracy.

In contrast, FIG. 14 contains graphs showing pickup voltage waveformsrelative to a magnetic field that is orthogonal to the direction ofmagnetic sensitivity when magnetic fields of 0 Oe through 10 Oe areapplied in orthogonal directions within the film plane in the fluxgatesensor of the above described example of the present invention in thesame way as is described above. It can be seen that by applying amagnetic field which is orthogonal to the direction of magneticsensitivity, the timings at which a pickup voltage is generated as wellas the peak height of the pickup voltage exhibit substantially nochange, and cross-axis sensitivity is extremely small. The reason forthis is that, in addition to the broad-width end portions at both endsof the core being designed such that the shape anisotropy caused by thediamagnetic field coincides with the longitudinal direction of the core,namely, with the direction of magnetic sensitivity of the sensor, butalso because the end portions are in an extremely excited state in thedirection of magnetic sensitivity, they are largely unaffected by anymagnetic field from an orthogonal direction.

In the case of a fluxgate sensor, it is possible to broaden themeasurement magnetic field range of the sensor by using an excitationcurrent and, as is shown in FIG. 10, it is possible to secure a broadmeasurement magnetic field range of 10 Oe or more while maintainingexcellent linearity. By providing a broad measurement magnetic fieldrange in this manner, it becomes possible to obtain a wide calibrationrange for the offset magnetic field.

At this time, by reducing the effects on magnetic fields which areorthogonal to the direction of magnetic sensitivity of the sensor, itbecomes possible to increase the calibration accuracy of an offsetmagnetic field in a wide range magnetic field, and to improve the degreeof freedom in the placement of components within an instrument.

Second Preferred Embodiment

FIG. 12 illustrates how excitation coils and a detection coil are woundin a fluxgate sensor according to a second preferred embodiment of thepresent invention.

In the first preferred embodiment, the excitation coils are only woundonto the broad-width end portions 1 at the two ends of the magneticcore. In contrast to this, in the second preferred embodiment, the firstsolenoid coils 9, which are excitation coils, are wound not only ontothe broad-width end portions 1 at the two ends, but also onto thenarrow-width center portion 2. Namely, the excitation coils are woundover the entire circumference of the magnetic core, and the secondsolenoid coil 10, which is a detection coil, is only wound onto thecenter portion 2 of the magnetic core. In this winding mode as well, thesame operating effects as in the above described first preferredembodiment are obtained.

Third Preferred Embodiment

A third preferred embodiment of the present invention will now bedescribed.

The magnetic core of a fluxgate sensor according to a third preferredembodiment of the present invention has the same structure as that ofthe fluxgate sensor according to the first preferred embodiment of thepresent invention, however, it differs in the operation of the solenoidcoil. Namely, in the same way as in the first preferred embodiment ofthe present invention, the magnetic core of the fluxgate sensoraccording to the third preferred embodiment of the present invention hasan H-shape such as that shown in FIGS. 1A and 1B. The magnetic core ofthe fluxgate sensor according to the third preferred embodiment of thepresent invention has end portions 1 and a center portion 2. The width Bof the end portions 1 is wider than that of the width C of the centerportion 2. Unlike the first preferred embodiment of the presentinvention, however, in the third preferred embodiment of the presentinvention, the first solenoid coils which are wound around thecircumference of the end portions 1 are pickup coils. The secondsolenoid coil which is wound around the circumference of the centerportion 2 is an excitation coil.

In the same way as the first preferred embodiment of the presentinvention, a top view of the fluxgate sensor according to the thirdpreferred embodiment of the present invention is the same as the viewshown in FIG. 4. However, unlike the first preferred embodiment of thepresent invention, in the third preferred embodiment of the presentinvention, the first solenoid coils 9 are pickup coils, and the secondsolenoid coil 10 is an excitation coil. The narrow-width center portion2 of the excitation coil 3 is excited when power is supplied to thesecond solenoid coil 10 which is wound around the circumference thereof.In contrast, induced voltage is applied to the broad-width end portions1 of the magnetic core 3, and this induced voltage is detected by thefirst solenoid coils 9 that are wound around the circumference of theend portions 1.

The method of manufacturing the fluxgate sensor according to the thirdpreferred embodiment of the present invention is the same as that usedin the first preferred embodiment of the present invention. In thefluxgate sensor according to the third preferred embodiment of thepresent invention as well, the same operating effects as in the abovedescribed first preferred embodiment are obtained.

The fluxgate sensor of the present invention can be used as a smallsized magnetic sensor. Moreover, this magnetic sensor can be widely usedas an electronic compass in mobile telephones, portable navigationdevices, game controllers, and the like.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as limited by theforegoing description and is only limited by the scope of the appendedclaims.

1. A fluxgate sensor comprising: a first wiring layer that is formed ona substrate; a first insulating layer that is formed so as to cover thefirst wiring layer; a magnetic core that is formed on the firstinsulating layer, and that includes a center portion, and first andsecond end portions that are continuous with the center portion and havea broader width than the width of the center portion, and are positionedat the two ends of the center portion; a second insulating layer thatcovers the magnetic core, and is formed on the first insulating layer;and a second wiring layer that is formed on the second insulating layer,wherein the first wiring layer and the second wiring layer have aplurality of wires that are substantially parallel to each other, andthe two ends of the wires of the first wiring layer and of the wires ofthe second wiring layer are electrically connected together via portionswhere the first insulating layer and the second insulating layer havebeen selectively removed, and spiral-shaped first solenoid coils arewound around the first and second end portions, and a spiral-shapedsecond solenoid coil is wound around the center portion.
 2. The fluxgatesensor according to claim 1, wherein a value of a ratio B/D between awidth B of the first and second end portions and a length D of thelongitudinal direction of the first and second end portions is lessthan
 1. 3. The fluxgate sensor according to claim 1, wherein the firstsolenoid coil contains a third solenoid that is wound around the firstend portion and a fourth solenoid coil that is wound around the secondend portion, and the third solenoid coil and the fourth solenoid coilare connected together in series, and have substantially the same numberof winds.
 4. The fluxgate sensor according to claim 1, wherein the firstsolenoid coil is wound around the center portion and the first andsecond end portions.
 5. An electronic compass comprising: a substrate;and first, second, and third fluxgate sensors that are located on thesubstrate, and that are aligned respectively with three axes, whereineach of the first, second, and third fluxgate sensors includes: a firstwiring layer that is formed on a substrate; a first insulating layerthat is formed so as to cover the first wiring layer; a magnetic corethat is formed on the first insulating layer, and that includes a centerportion, and first and second end portions that are continuous with thecenter portion and have a broader width than the width of the centerportion, and are positioned at the two ends of the center portion; asecond insulating layer that covers the magnetic core, and is formed onthe first insulating layer; and a second wiring layer that is formed onthe second insulating layer, and wherein the first wiring layer and thesecond wiring layer have a plurality of wires that are substantiallyparallel to each other, and the two ends of the wires of the firstwiring layer and of the wires of the second wiring layer areelectrically connected together via portions where the first insulatinglayer and the second insulating layer have been selectively removed, andspiral-shaped first solenoid coils are wound around the first and secondend portions, and a spiral-shaped second solenoid coil is wound aroundthe center portion.
 6. The electronic compass according to claim 5,wherein a value of a ratio B/D between a width B of the first and secondend portions and a length D of the longitudinal direction of the firstand second end portions is less than
 1. 7. The electronic compassaccording to claim 5, wherein the first solenoid coil contains a thirdsolenoid that is wound around the first end portion and a fourthsolenoid coil that is wound around the second end portion, and the thirdsolenoid coil and the fourth solenoid coil are connected together inseries, and have substantially the same number of winds.
 8. Theelectronic compass according to claim 5, wherein the first solenoid coilis wound around the center portion and the first and second endportions.
 9. A fluxgate sensor comprising at least: a first wiringlayer; a first insulating layer that is formed so as to cover the firstwiring layer; a magnetic core that is formed on the first insulatinglayer, and that is provided with a detection portion, and first andsecond excitation portions that are continuous with the detectionportion and have a broader width than the width of the detectionportion, and are positioned at the two ends of the detection portion; asecond insulating layer that covers the magnetic core, and is formed onthe first insulating layer; and a second wiring layer that is formed onthe second insulating layer, wherein the first wiring layer and thesecond wiring layer have a plurality of wires that are substantiallyparallel to each other, and the two ends of the wires of the firstwiring layer and of the wires of the second wiring layer areelectrically connected together via portions where the first insulatinglayer and the second insulating layer have been selectively removed, andspiral-shaped excitation coils are wound around the first and secondexcitation portions.
 10. The fluxgate sensor according to claim 9,wherein the excitation coils contain a first excitation coil that iswound around the first excitation portion, and a second excitation coilthat is wound around the second excitation portion, and the firstexcitation coil and the second excitation coil are connected together inseries such that the magnetic fields they generate are aligned in thesame direction.
 11. The fluxgate sensor according to claim 9, whereinthe excitation coils are wound around the excitation portions and thedetection portion that is formed in the center portion of the magneticcore.
 12. An electronic compass in which three of the fluxgate sensorsaccording to claim 9 are located on a single substrate, so as to bealigned respectively with three axes.